1. Field of the Invention
A toroidal type continuously variable transmission according to the present invention is used as, for example, an automatic transmission for an automobile. In particular, the present invention is intended to improve the durability of a power roller section constituting such a toroidal type continuously variable transmission.
In addition, of the toroidal type continuously variable transmissions used as, for example, transmissions for automobiles, the present invention relates to the improvement of a double-cavity toroidal type continuously variable transmission having two power transmission paths in parallel.
2. Related Background Art
The use as a transmission for an automobile of a toroidal type continuously variable transmission such as that shown in FIGS. 7 and 8 is being researched. As disclosed in, for example, Japanese Utility Model Laid-Open No. 62-71465, this toroidal type continuously variable transmission supports an input-side disc 2 concentrically with an input shaft 1 and fixes an output-side disc 4 to the end of an output shaft 3 arranged concentrically with the input shaft 1. A plurality of (normally two or three) trunnions 6, 6 that oscillate around pivots 5, 5 are provided inside a casing in which the toroidal type continuously variable transmission is accommodated. Relative to the axial direction (the lateral direction in FIGS. 7 and 8) of the input- and output-side discs 2 and 4, the pivots 5, 5 are located between the discs 2 and 4, in the direction perpendicular to the axial direction of the discs 2 and 4, at a torsional position relative to the central axis of the discs 2 and 4.
That is, the trunnions 6, 6 each have the pivot 5 on the outer side at either end thereof in such a way that each pivot is concentric with the corresponding trunnion. In addition, the proximal end of displacement shaft 7, 7 is supported by the trunnion 6, 6 in its intermediate portion, and each trunnion 6 can be oscillated around the corresponding pivot 5, 5 to adjust the inclination of the corresponding displacement shaft 7, 7. A power roller 8, 8 is rotatably supported around the displacement shaft 7, 7 supported on the trunnion 6, 6. The power roller 8, 8 is sandwiched between the discs 2 and 4 on the input and output sides. The opposed inner sides 2a and 4a of the input- and output-side discs 2 and 4 each have a cross section consisting of a recessed surface obtained by rotating around the input and output shafts 1 and 3 an circular arc drawn around a point on the pivot 5. The circumferential surface 8a, 8a of the power roller 8, 8 that is formed like a spherically protruding surface is abutted on the inner sides 2a and 4a.
A loading cam pressure apparatus 9 is provided between the input shaft 1 and the input-side disc 2 so as to elastically press the input-side disc 2 toward the output-side disc 4. The pressure apparatus 9 is composed of a cam plate 10 rotating with the input shaft 1 and a plurality of (for example, four) rollers 12, 12 held by a holder 11. A cam surface 13 that is a recessed and protruding surface extending in the circumferential direction is formed on one side (the left side in FIGS. 7 and 8) of the cam plate 10, and a similar cam surface 14 is formed on the outer side (the right side in FIGS. 7 and 8) of the input-side disc 2. The plurality of rollers 12, 12 are rotatably supported around the respective axes located in the radial direction relative to the center of the input shaft 1.
During the use of a toroidal type continuously variable transmission of this configuration, when the cam plate 10 is rotated in response to the rotation of the input shaft 1, the cam surface 13 presses the plurality of rollers 12, 12 against the cam surface 14 on the outer surface of the input-side disc 2. Consequently, the input-side disc 2 is pressed against the power rollers 8, 8, while being rotated due to the pressing of the pair of cam surfaces 13 and 14 against the rollers 12, 12. The rotation of the input-side disc 2 is transmitted to the output-side disc 4 via the power rollers 8, 8 to rotate the output shaft 3 fixed to the output-side disc 4.
If the rotational speed ratio (transmission ratio) between the input and output shafts 1 and 3 is changed and if the speed is first reduced between the input and output shafts 1 and 3, the trunnions 6, 6 are oscillated around the pivots 5, 5 to incline the displacement shafts 7, 7 in such a way that the circumferential surfaces 8a, 8a of the power rollers 8, 8 abut on that portion of the inner side 2a of the input-side disc 2 which is closer to its center and that portion of the inner side 4a of the output-side disc 4 which is closer to its outer circumference, respectively, as shown in FIG. 7. Conversely, to increase the speed, the trunnions 6, 6 are oscillated around the pivots 5, 5 to incline the displacement shafts 7, 7 in such a way that the circumferential surfaces 8a, 8a of the power rollers 8, 8 abut on that portion of the inner side 2a of the input-side disc 2 which is closer to its outer circumference and that portion of the inner side 4a of the output-side disc 4 which is closer to its center, respectively, as shown in FIG. 8. By setting the inclination of each displacement shaft 7, 7 at an intermediate between the values of inclinations in FIGS. 7 and 8, an intermediate transmission ratio can be obtained between the input and output shafts 1 and 3.
Furthermore, FIGS. 9 and 10 show a more specific toroidal type continuously variable transmission described in the micro film of Japanese Utility Model Application No. 63-69293 (Japanese Utility Model Application Laid-Open No. 1-173552). The input-side and output-side discs 2 and 4 are rotatably supported around an input shaft 15 via needle bearing 16, 16, respectively. The cam plate 10 spline-engages the outer circumferential surface of the input shaft 15 located at its end (the left end in FIG. 9) and is prevented by a collar (flange) portion 17 from being moved in a direction in which it leaves the input-side disc 2. Thus, a loading cam pressure apparatus 9 is provided wherein due to the rotation of the input shaft 15, the cam plate 10 and the rollers 12, 12 press the input-side disc 2 toward the output-side disc 4 while rotating the input-side disc 2. An output gear 18 is coupled to the output-side disc 4 using keys 19, 19 so that the output-side disc 4 and the output gear 18 rotate in synchronism. The output gear 18 and other gears (not shown) meshing with the output gear 18 constitute a power output means for rotating the output-side disc 4.
The pivots 5, 5 provided at the respective ends of the pair of trunnions 6, 6 are supported on support posts 20, 20 so as to oscillate and to be displaced in the axial direction (the direction perpendicular to the sheet of FIG. 9 or the lateral direction in FIG. 10). The pair of support posts 20, 20 comprise metal sheets of a sufficient rigidity and are supported inside a casing 22 so as to oscillate and to be displaced in the axial direction of the pivot 5, 5 by externally fitting a circular hole 21 formed in the center of the support post on support pins 24a and 24b fixed to the inner surface of the casing 22 or a side of a cylinder case 23 provided inside the casing 22. A circular support hole 25, 25 is formed at the ends of the support post 20, 20 and the pivot 5, 5 is supported in the support hole 25, 25 via a radial needle bearing 27, 27 including an outer ring 26, 26. Based on this configuration, the trunnion 6, 6 is supported inside the casing 22 so as to oscillate around the pivot 5, 5 and to be displaced in the axial direction thereof.
The displacement shaft 7, 7 is supported in a circular hole 40, 40 formed in the intermediate portion of each trunnion 6, 6 supported inside the casing 2, 2 as described above. The displacement shafts 7, 7 have support shaft sections 28, 28 that are mutually parallel and eccentric and pivot sections 29, 29, respectively. The support shaft section 28, 28 is oscillatorily supported inside the circular hole 40, 40 via a radial needle bearing 30, 30. In addition, the power roller 8, 8 is rotatably supported around the pivot section 29, 29 via a radial needle bearing 31, 31.
The pair of displacement shafts 7, 7 are provided at 180.degree. from each other around the input shaft 15. The pivot section 29, 29 of the displacement shaft 7, 7 is eccentric to the support shaft section 28, 28 in the same direction relative to the rotating direction of the input- and output-side disc 2 or 4 (the lateral direction in FIG. 10). The eccentric direction is almost perpendicular to the direction in which the input shaft 15 is disposed (the lateral direction in FIG. 9 or the direction perpendicular to the sheet of FIG. 10). Thus, the power roller 8 is supported so as to be slightly displaced in the direction in which the input shaft 15 is disposed. As a result, even if the power roller 8 tends to be displaced in the axial direction (the lateral direction in FIG. 9 or the direction perpendicular to the sheet of FIG. 10) of the input shaft 15 due to the difference in the dimensional accuracy of components or elastic deformation during power transmission, this displacement can be absorbed without effecting excessive force on the components.
A thrust rolling bearing such as a thrust ball bearing 32, 32 and a thrust bearing such as a thrust needle bearing 34, 34 bearing thrust loads on an outer ring 33, 33 which is described below, are provided between the outer side of the power roller 8, 8 and the inner side of the intermediate portion of the trunnion 6, 6 in this order from the outer side of the power roller 8, 8. The thrust ball bearing 32, 32 corresponds to a thrust rolling bearing according to this invention, and bears loads on the power roller 8, 8 in the thrust direction while allowing the power roller 8, 8 to rotate. In addition, the thrust needle bearing 34, 34 bears thrust loads provided by the power roller 8, 8 to the outer ring 33, 33 of the thrust ball bearing 32, 32 while allowing the pivot section 29, 29 and the outer ring 33, 33 to oscillate around the support shaft section 28, 28.
A drive rod 35, 35 is coupled to one end of each trunnion 6, 6 (the left end in FIG. 10), and a piston 36, 36 is fixed to the outer circumferential surface of the intermediate portion of the drive rod 35, 35. Each drive piston 36, 36 is fitted in a drive cylinder 37, 37 provided in the cylinder case 23 in an oil tight manner. Furthermore, a pair of rolling bearings 39, 30 are provided between a support wall 38 provided inside the casing 22 and the input shaft 15 so as to rotatably support the input shaft 15 in the casing 22.
In the toroidal type continuously variable transmission configured as described above, the rotation of the input shaft 15 is transmitted to the input-side disc 2 via the pressure apparatus 9. The rotation of the input-side disc 2 is transmitted to the output-side disc 4 via the pair of power rollers 8, 8, and the rotation of the output-side disc 4 is obtained through the output gear 18. To vary the rotational-speed ratio between the input shaft 15 and output gear 18, the pair of drive pistons 36, 36 are displaced in the opposite directions. When the drive pistons 36, 36 are displaced, the pair of trunnions 6, 6 are displaced in the opposite directions, thereby, for example, displacing the power roller 8 in the lower part of FIG. 10 rightward in this figure, while displacing the power roller 8 in the upper part of FIG. 10 leftward in this figure. Consequently, the direction of the tangential force changes that acts on the abutting portions of the circumferential surface 8a, 8a of the power roller 8, 8 and of the inner sides 2a and 4a of the input- and output-side discs 2 and 4. This change in the direction of the force causes the trunnions 6, 6 to oscillate in the opposite directions in FIG. 9 around the pivots 5, 5 pivotably supported on the support posts 20, 20. As a result, as shown in FIGS. 7 and 8 described above, the abutting positions of the circumferential surfaces 8a, 8a of the power rollers 8, 8 and of the inner sides 2a and 4a change to change the rotational-speed ration between the input shaft 15 and the output gear 18.
Due to the elastic deformation of the components during power transmission, when the power roller 8, 8 is displaced in the axial direction of the input shaft 15, the displacement shaft 7, 7 pivotably supporting the power roller 8, 8 slightly oscillates around the support shaft section 28, 28. This oscillation causes the outer side of the outer ring 33, 33 of the thrust ball bearing 32, 32 and the inner side of the trunnion 6, 6 to be displaced relatively. Due to the presence of the thrust needle bearing 34, 34 between these outer and inner surfaces, only a small force is required to effect this relative displacement. Accordingly, only a small force is required to change the inclination of the displacement shaft 7, 7, as described above.
During the operation of the toroidal type continuously variable transmission having the above configuration and operating as described above, a large complicated force is repeatedly applied to both input- and output-side discs 2 and 4 due to the pressing of the power rollers 8, 8 on the discs. For example, during the operation of the toroidal type continuously variable transmission, a thrust load F is provided by the power roller 8 to the inner side 4a of the output-side disc 4 at a point A in FIG. 11. Such a thrust load causes the output-side disc 4 to be elastically deformed to concentrate a large tensile stress in portions B, C, and D in FIG. 11. The sites on which the tensile stress is effected move in the circumferential direction due to the rotation of the output-side disc 4 in response to the operation of the toroidal type continuously variable transmission. Thus, a large tensile stress is repeatedly effected on a portion present in the circumferential direction. Almost the same situation occurs in the input-side disc 2.
The tensile stress repeatedly effected on both input- and output-side discs 2 and 4 damages the discs 2 and 4, for example, cracks them, resulting in destruction. Thus, to provide the toroidal type continuously variable transmission with a sufficient durability, the input- and output-side discs 2 and 4 must be prevented from damage such as cracks despite the tensile stress described above.
If the inner sides 2a and 4a of the input- and output-side discs that are abutted on by the circumferential surfaces 8a, 8a of the power rollers 8, 8 are vibrated in response to the rotation of the discs 2 and 4, respectively, the abutting condition between the circumferential surfaces 8a, 8a and the inner sides 2a and 4a becomes unstable. As a result, vibration may occur during the operation of the toroidal type continuously variable transmission, the speed change states of the power rollers 8, 8 may not be matched, or hunting may occur. Then, due to the vibration, mismatch in speed change state, or hunting, an excessive force is applied to the inner surfaces 2a and 4a abutting on the circumferential surfaces 8a, 8a to degrade the durability of the input- and output-side discs 2 and 4, for example, to cause the inner surfaces 2a and 4a to be peeled off too early.
A toroidal type continuously variable transmission according to this invention is provided in view of this problem.
In order to increase transmissible torque, a double-cavity-type toroidal type continuously variable transmission has been contemplated in which input-side discs 102A and 102B that are outer discs and output-side discs 104, 104 that are intermediate discs are provided around an input shaft 115 corresponding to a rotating shaft according to this invention in such a way that the input-side discs 102A and 102B and the output-side discs 104, 104 are arranged in parallel in the power transmission direction, as shown in FIG. 12. In the structure shown in FIG. 12, an output gear 118a is supported around the intermediate portion of the input shaft 115 so as to rotate around the shaft 115, and the output-side discs 104, 104 are spline-engaged with the respective ends of the output gear 118a. A needle bearings 116, 116 is provided between the inner circumferential surface of each output-side disc 104, 104 and the outer circumferential surface 115 of the input shaft 115 so that the output-side disc 104 is supported around the input shaft 115 so as to rotate around the shaft 115 and to be displaced in the axial direction of the shaft 115. In addition, the input-side discs 102A and 102B are supported at the respective ends of the input shaft 115 so as to rotate with this shaft 115.
One 102A (in the left of FIG. 12) of the input-side discs has its rear surface (the left surface in FIG. 12) abutting on a loading nut 132 to hinder its axial (the lateral direction in FIG. 12) displacement relative to the input shaft 115. On the contrary, the input-side disc 102B opposed to the cam plate 110 is supported on the input shaft 115 via ball splines 133 so as to be displaced in the axial direction. A template spring 134 and a thrust needle bearing 135 are provided in series between the rear surface (the right surface in FIG. 12) of the input-side disc 102B and the front surface (the left surface in FIG. 12) of the cam plate 110. The template spring 134 acts as a pre-loading apparatus for applying a pre-load to the abutting portions of the inner sides 102a and 104a of the discs 102A, 102B, and 104 and the circumferential surfaces 108a, 108a of the power rollers 108, 108.
During the double-cavity-type toroidal type continuously variable transmission of the above configuration, the rotation of the input shaft 115 is transmitted from the pair of input-side discs 102A and 102B to the pair of output-side discs 104, 104 via the plurality of (In the illustrated example, four, that is, two for each pair; but this number may be six, that is, three for each pair) power rollers 108, 108. The rotational power transmitted to the pair of output-side discs 104, 104 is transmitted to the single output gear 118a and is obtained from another gear (not shown) with which the output gear 118a is meshed. Since the rotational force is transmitted from the input shaft 115 to the output gear 118a through two paths arranged in parallel, a large rotational force (torque) can be transmitted. To change the speed change ratio between the input shaft 115 and the output gear 118a, the trunnion 106 bearing the displacement shaft 107 is moved parallel to incline the displacement shaft 107 bearing the power roller 108. A structure for moving the trunnion 106 parallel is the same as in the single-cavity-type toroidal type continuously variable transmission shown in FIGS. 9 and 10. In the double-cavity-type toroidal type continuously variable transmission, however, the supply and ejection of pressure oil to and from the drive cylinders is switched to keep the amounts and directions of movement of the trunnions 106, 106 in synchronism.
In the double-cavity-type toroidal type continuously variable transmission shown in FIG. 12, the pair of output-side discs 104, 104 that are intermediate discs are separate from the output gear 118a, and the pair of output-side discs 104, 104 are spline-engaged with the respective ends of a sleeve section 136 provided at the center of the output gear 118a. This configuration increases the number of components, thereby making the manufacturing, management, and assembly of parts cumbersome and increasing the axial sizes of the installed portions of the pair of output-side discs 104, 104 and output gear 118a.
The increase in the axial sizes of the installed portions increases the axial length of the input shaft 115, thereby increasing the interval between the pair of input-side discs 102A and 102B supported at the respective ends of the input shaft 115. Likewise, the increase in the interval between the pair of input-side discs 102A and 102B increases the amount of the torsional deformation of the input shaft 115 between the input-side discs 102A and 102B during the transmission of rotations, thereby increasing the phase difference between the input-side discs 102A and 102B in the rotating direction. As a result, it becomes difficult to synchronize the transmission of rotations between the input-side disc 102A and the output-side disc 104 in one of the cavities with the transmission of rotations between the input-side disc 102B and the output-side disc 104 in the other cavity, so the efficiency of the double-cavity-type toroidal type continuously variable transmission cannot be ensured easily.
U.S. Pat. No. 2,140,012 describes a structure wherein both axial sides of a single output-side disc corresponding to an intermediate disc are formed as recessed surfaces of a circular cross section and wherein the circumferential surfaces of power rollers are abutted on the recessed surfaces. In this structure described in the U.S. Patent specification, the rotation of the output-side disc is obtained through a cylindrical bottomed drum having at one end an opening that is coupled and fixed to the output-side disc and incorporating one of the input-side discs inside. Thus, it is very difficult to support a power roller provided between one of the input-side discs and the intermediate disc, the structure is very complicated, and a support structure for the power roller must be located inside the drum. Thus, the power roller section including this support structure must be miniaturized. In addition to the need to miniaturize the power roller section, the limited amount of power that can be transmitted by the drum prevents a sufficiently large rotational force from being transmitted.
A method for manufacturing a toroidal type continuously variable transmission and an intermediate disc for the toroidal type continuously variable transmission according to this invention has been invented to eliminate all these inconveniences.